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Carbon Composite?

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  • Carbon Composite?

    Has anyone here ever dabbled with laying up carbon composites? I'm looking for information and first hand advice for wet lay-up and vacuum bagging in particular. Also, any ideas or sources for an inexpensive vacuum pump would be most helpful.



  • #2
    Glen, how big a part, and how much shape does it have? What is the tightest radius on the part, and where are you at? Have a plastics guru sitting in my cube, would be willing to give you some pointers. Shawn


    • #3
      The intake side of your air compressor.

      American Science and Surplus had some used vacuum pumps.


      • #4
        Take a look at the CAD pictures here to see what I'm up to.


        I want to assemble custom bicycle frames from existing carbon tubes and join them by laying up carbon from one side (with some plates down the center) then when it's set lay up from the opposite side and trim off the excess. I'd be using a high drapable cloth and vacuum bagging each side.


        • #5
          Glen, I've worked as a composite toolmaker for an aerospace manufacturer and have experience with carbon, aramid, and glass both wet and pre-preg both vacum and traditional layups.

          As a starting point how much experience do you have with this type of layup?

          If I understand you corectly you're making the lugs for a bike frame using off the shelf tubing for the frame correct? And you want to make each lug in two halves layed up in place correct? If I am correct in my understanding I wouyld stongly advise against this course of action. If not then please clarify.

          As for a vacum source you can use a vacume genarator run off an air compressor or if your willing use your car engine at idle and pull vacum off of the intake manifold. At idle you should get more than 22"Hg. Obviously you need to make sure there is no danger of CO accumulation and be willing to run your car at idle for an extended period of time. Renting a vacum pump from a composite supplier might be an option as well since neither of the alternatives mentioned will produce as much vacum as a dedicated pump.

          You didn't mention it, but be sure to incorperate peal ply and a bleeder cloth into your layup for best results.

          I'll be around for a while but I've got my daughter this weekend as well so I might not be responding too quickly for the next couple days.



          • #6
            Hi Glenn,
            These parts look like a good candidate for two piece compression tools. Use clearance wax and lay up the backside. The radii as seen on your photo page make bagging iffy at best. Go to your local tooling supply shop and they can set you up with all the stuff. If you have a buissiness or a school project, ask for free samples from the manufacturers, don't be shy. They can give you tons of free advice and free stuff. Try Tool Chemical or Ren Plastics.


            • #7

              Thanks for the information. I am aware of the need for perforated release film and bleed cloth etc. My experience however lies more in cutting and welding thin wall steel tubing for frame building. Your advice would be more than welcome. One of the reasons I posted to this board is the vast variety of experience here.

              You are correct, I was thinking of laying up one side of the lug in place and then the other when the first was cured. I am concerned about shrinkage of the layup affecting alignment but not sure how much of an issue that would be.

              Could, when you have time, elaborate on why you advise against this method. There is another company building frames using a similar method ( but they squeeze the joints between aluminum tools. I was hoping to have more freedom with joint design and avoid the dedicated tooling expense.

              Any suggestions or alternative methods of creating joints oriented like I have in the photos


              would be much appreciated. Thanks for any help you can provide.



              • #8
                I had considered using low melting temp alloy (Woods metal etc) to make compression tooling for each joint. I imagine clearance wax would melt below the 158F that the alloy goes liquid.

                I was worried about the radii of the bends using a vacuum process. Thanks for the heads up.


                • #9
                  Clamshell tooling would certainly give you a better finish, a necesity if you're thinking of selling these frames. It also gives better results than bagging. I disagree that this could not be bagged with a little forthought but it would take a little practice.

                  Simply stated my objection to the design is that it is prone to failure and negates any advantage provided by the use of composite material. Keep a couple things in mind: 1) Composite material is just that, a composite of fiber and a matrix in which to encapsulate it. 2) The fiber's streangth is not omni-directional, depending on its construction it only exhibits streangth in one or two axis. Stated planely the lamination itself can be easily broken. 3) The matrix (epoxy resin) achives its streangth through polimerizing, forming long chains though chemichal reaction. When applied to an already cured surface it can only bind via mechanichal bonds. It will never become integral with the surface it is applied to but is limited to atachment via small surface imperfections it has worked itself into.

                  By forming the lugs in two halves you not only do not have the streangth of the carbon fibers working for you but you do not even have the full streangth of the epoxy. If you have any experience as a woodworker think of this joint being made out of a block of wood. Functionaly you have run the tubing in the same plane as the wood grain. Any loading will work the grain apart until it fails.

                  As you are aware the lugs are the area of a bike frame prone to the greatest concentration of stress. I'm sure you're also aware that just because someone makes and markets a product does not mean it's safe. Given that thes are doubtless intended as high preformance frames and prone to severe duity I would strongly caution you to reconsider the design. I'm guessing that you are trying to take advantage of the additional rigidity the flange would provide. Remember that an increase in ridgity will also serve to concetrate load rather than distribute it, making the need for a sound joint all the more desirable. It is possible to incorperate this feature into a one piece lug.

                  You will also need to incorperate larger radius into the flange, carbon fiber does not like to form itself into small radiusus. There are a couple of solutions to this problem.



                  • #10
                    Do you have any close up photos of the other frame lugs? Their web site doesn't seem to show anything in detail.


                    • #11
                      Here's a guy who vacuum bags using a Tilia foodsaver:


                      Haven't tried it yet, but I bought a Tilia, and will give it a try when I get the time.



                      • #12
                        Just a quick scan of the page doesn't state how much vacuum the food saver would pull, anybody know?


                        • #13

                          The existing frames constructed this way (Calfee Design) are well regarded and come with a lifetime warrantee so they must be doing something right. I don't have any close up shots of their joints.

                          I do know that the bond between the lug and tube will not be taking advantage of the carbon but will be a simple glue joint. Trek makes all their carbon frames from carbon tubes glued to internal carbon lugs.

                          I'd like to figure out a simple method for forming the joints without the webs if it could be done with inexpensive tooling and have an acceptable finish. The plan would be to clear coat the whole frame so joint finish is not super critical.

                          Whatever method I went with I plan to test joints to failure prior to building an entire frame.

                          I guess I have a bit more investigation to do.

                          Thanks again for all the info.



                          • #14

                            If you do decide to make tooling, Devon has a line of industrial putties that work well.

                            Aluminum Putty is designed to work at 250F continuous:

                            Titanium Putty is designed for 350F continuous:

                            I haven't tried the Titanium Putty, but the Aluminum Putty is really nice. It's about as thick as peanut butter (like Jif without nuts). Once in place it does not move, sag or flow out of position. Turns, bores, faces & finishes much like solid aluminum. Pretty handy for prototype work where you may want to change features and dimensions.

                            Barry Milton

                            [This message has been edited by precisionworks (edited 03-18-2005).]
                            Barry Milton


                            • #15
                              It's not the lug to tube joint that concerns me, it's failure of the lug itself. Are you CERTAIN that Calfee is making the lugs in two pieces? I don't mean to sound like a wet blanket, but I honestly can't think of a weaker way to produce this part with the exception of excluding the flange and butting the cloth ends together at the parting line.

                              I'd like to get a little better understanding of your reasons for going this route. Are you thinking of building custom frames and want to be able to change frame geometry without having to re-tool? There are some ways around that. If the flanges are not critical then why not make a single layup around the tubes? Even if the flanges are key they can be incorporated with a little planning. Would you consider making the lugs as seperate pieces and then potting the tubes in place?